High power electrode materials

ABSTRACT

An LFP electrode material is provided which has improved impedance, power during cold cranking, rate capacity retention, charge transfer resistance over the current LFP based cathode materials. The electrode material comprises crystalline primary particles and secondary particles, where the primary particle is formed from a plate-shaped single-phase spheniscidite precursor and a lithium source. The LFP includes an LFP phase behavior where the LFP phase behavior includes an extended solid-solution range.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 16/575,256, entitled “HIGH POWER ELECTRODE MATERIALS,” filed onSep. 18, 2019. U.S. patent application Ser. No. 16/575,256 is adivisional of U.S. patent application Ser. No. 15/495,886, entitled“HIGH POWER ELECTRODE MATERIALS,” filed on Apr. 24, 2017, now U.S. Pat.No. 10,522,833. U.S. patent application Ser. No. 15/495,886 is adivisional of U.S. patent application Ser. No. 14/641,172, entitled“HIGH POWER ELECTRODE MATERIALS,” filed Mar. 6, 2015, now U.S. Pat. No.9,660,267. U.S. patent application Ser. No. 14/641,172 is is acontinuation-in-part of U.S. patent application Ser. No. 12/885,907,entitled “FERRIC PHOSPHATE AND METHODS OF PREPARATION THEREOF,” filedSep. 20, 2010, which claims priority to U.S. Provisional PatentApplication No. 61/264,951, entitled “FERRIC PHOSPHATE AND METHODS OFPREPARATION THEREOF,” filed Nov. 30, 2009, and U.S. Provisional PatentApplication No. 61/243,846, entitled “FERRIC PHOSPHATE DIHYDRATE ASLITHIUM IRON PHOSPHATE SYNTHETIC PRECURSOR AND METHOD OF PREPARATIONTHEREOF,” filed Sep. 18, 2009. U.S. patent application Ser. No.14/641,172 also claims priority to U.S. Provisional Patent ApplicationNo. 61/949,596, entitled “HIGH POWER ELECTRODE MATERIALS,” filed Mar. 7,2014, and U.S. Provisional Patent Application No. 62/103,987, entitled“HIGH POWER ELECTRODE MATERIALS,” filed Jan. 15, 2015, the entirecontents of each of which are hereby incorporated by reference for allpurposes.

FIELD OF THE INVENTION

This application relates to materials and methods for batteryelectrodes, materials used therein, and electrochemical cells using suchelectrodes and methods of manufacture, such as lithium secondarybatteries.

BACKGROUND AND SUMMARY

Lithium-ion (Li-ion) batteries are a type of rechargeable battery whichproduce energy from electrochemical reactions. In a typical lithium ionbattery, the cell may include a positive electrode, a negativeelectrode, an ionic electrolyte solution that supports the movement ofions back and forth between the two electrodes, and a porous separatorwhich allows ion movement between the electrodes and ensures that thetwo electrodes do not touch.

Li-ion batteries may comprise metal oxides for the positive electrode(herein also referred to as a cathode) and carbon/graphite for thenegative electrode (herein also referred to as an anode), and a salt inan organic solvent, typically a lithium salt, as the ionic electrolytesolution. During charge the anode intercalates lithium ions from thecathode and during discharge releases the ions back to the cathode.Recently, lithium metal phosphates, for example lithium iron phosphates,have found use as a cathode electroactive material.

The use of lithium iron phosphate (LFP) provides a next generationreplacement for the more hazardous lithium cobalt oxide that iscurrently used in commercial lithium ion batteries. Li-ion batteriesusing LFP based cathode materials may currently be found in cordlesshand tools and on-board UPS devices. Battery packs have recently beendemonstrated for transportation including aviation and electric vehiclesas well as plug-in hybrid electric vehicle automobiles and buses.

The characteristics for current LFP materials for use in batteries areoften different from or in contradiction with those for other intendedpurposes. Impurities which may be present due to the synthesis may bedetrimental to Li-ion batteries. Furthermore, different batches duringsynthesis of commercially available LFP materials may often haveinconsistent properties. Thus, an LFP material with carefully controlledcharacteristics is needed which provides consistent and desirableproperties for use in Li-ion batteries.

Current LFP materials for use in Li-ion batteries are synthesized fromvarious starting reagents and have a range of characteristics. Forexample, in U.S. Pat. No. 8,541,136 (Beck et al) provides an LFPmaterial which includes excess lithium and a surface area of 45.5 m²/gto improve discharge rate capabilities. In another example, US2011/006829 (Beck et al) provides a high purity crystalline phase LFPwhich is synthesized from a high purity crystalline ferric phosphatematerial, hereby incorporated by reference for all purposes.

However, the inventors herein have recognized potential issues with thecurrent generation of LFP based cathode materials. The current LFPmaterials may have limited use in extreme temperature environments, suchas exposure to temperature at or below 0° C., as the energy of theLi-ion battery may be too low. Thus, the LFP materials for use in Li-ionbatteries need improvements in energy in extreme temperatureenvironments to be used in a broader range of applications. Further, itwas recognized that improvements with regards to impedance, power duringcold cranking, high rate capacity retention, and charge transferresistance would improve the current generation of LFP based cathodematerials.

One potential approach as found by the inventors to at least addresssome of the above issues includes synthesizing a plate-shapedspheniscidite precursor which can be used to produce an improvedelectrode material, also referred to as the LFP material. Theplate-shaped precursor may be formed as a single-phase material, and, insome embodiments, may have a surface area in a range of 20 m²/g to 25m²/g, as disclosed in U.S. Provisional Patent Application No.61/949,596, entitled “HIGH-POWER ELECTRODE MATERIALS,” filed Mar. 7,2014, the entire contents of which are hereby incorporated by referencefor all purposes.

The LFP material formed from the plate-shaped spheniscidite precursor,herein also referred to as an ammonium iron phosphate precursor, maycomprise crystalline primary and secondary particles. The primaryparticles may have a particle size between about 20 nm to about 80 nm.The secondary particles may have a d50 particle size in the range of 5microns to 13 microns. In some examples, the secondary particles mayhave a surface area of in a range of 25 m²/g to 35 m²/g. Further, thesecondary particles may have a tap density from about 0.8 g/mL to 1.4g/mL.

In some examples, the LFP material may contain less than about 5 weightpercent of any additional phase that does not substantially store ions.Further, the LFP material, in some embodiments, may have a carbonpercentage in the range of 2.1% to 2.5%.

As provided in detail in the description below, the disclosed LFPmaterial may provide improved battery properties in extreme temperatureenvironments. For example, the LFP material may have improved capacityat low temperature, wherein the low temperature may be at or below 0° C.Moreover, the LFP material provides for improved impedance, increasedpower during cold cranking, increased high rate capacity retention, andimproved charge transfer resistance.

It will be understood that the summary above is provided to introduce insimplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows an SEM image of the pure spheniscidite.

FIG. 1B shows an SEM image of the pure spheniscidite.

FIG. 2A shows an SEM image of the primary particle of the LFP activematerial produced using a solvent based system.

FIG. 2B shows an SEM image of the primary particle of the LFP activematerial produced using a water based system.

FIG. 3A shows an SEM image of the LFP active material using a solventbased system.

FIG. 3B shows an SEM image of the LFP active material using a waterbased system.

FIG. 4 illustrates an example method for synthesizing spheniscidite.

FIG. 5 shows a TGA curve of spheniscidite.

FIG. 6 shows an XRD pattern of pure spheniscidite.

FIG. 7 illustrates an example method for synthesizing LFP fromspheniscidite.

FIG. 8 shows an XRD pattern of LFP.

FIG. 9 shows a first charge capacity of the LFP synthesized fromspheniscidite compared to current LFP materials.

FIG. 10 shows a first discharge capacity of the LFP synthesized fromspheniscidite compared to current LFP materials.

FIG. 11 shows the percentage of first charge capacity loss of the LFPsynthesized from spheniscidite compared to current LFP materials.

FIG. 12 shows the absolute capacity loss of the LFP synthesized fromspheniscidite as compared to current LFP materials.

FIG. 13 shows an alternating current resistance impedance of the LFPsynthesized from spheniscidite compared to current LFP materials.

FIG. 14 shows a direct current resistance impedance of the LFPsynthesized from spheniscidite compared to current LFP materials.

FIG. 15 shows the capacity retention after 3 days of aging of the LFPsynthesized from spheniscidite compared to current LFP materials.

FIG. 16 shows the electrode thickness after formation.

FIG. 17 shows the hybrid pulse power characterization (HPPC) data at 23°C., at 1 s and 2 s direct current resistance of the LFP synthesized fromspheniscidite compared to current LFP materials.

FIG. 18 shows the hybrid pulse power characterization (HPPC) data at 23°C., at 10 s direct current resistance of the LFP synthesized fromspheniscidite compared to current LFP materials.

FIG. 19 shows the hybrid pulse power characterization (HPPC) data at−20° C., at 1 s and 20 s pulse power for the LFP synthesized fromspheniscidite compared to current LFP materials.

FIG. 20 shows the impedance in Double Layer Pouch (DLP) Cells at −20° C.for the LFP synthesized from spheniscidite compared to current LFPmaterials.

FIG. 21 shows the voltage profile at different 10 C rate discharge, forthe LFP synthesized from spheniscidite compared to current LFPmaterials.

FIG. 22 shows the normalized rate capability of the LFP synthesized fromspheniscidite compared to current LFP materials.

FIG. 23 shows the direct current resistance for the LFP synthesized fromspheniscidite compared to current LFP materials.

FIG. 24 shows the power resulting from a cold crank test at −30° C. forthe LFP synthesized from spheniscidite compared to current LFPmaterials.

FIG. 25 shows the alternating current impedance for the LFP synthesizedfrom spheniscidite compared to current LFP materials.

FIG. 26 shows an example electrode assembly.

FIG. 27A shows a wound cell example.

FIG. 27B shows a wound cell example.

FIG. 28 shows a XRD of the LFP synthesized from spheniscidite comparedto current LFP materials.

FIG. 29 is an example schematic phase diagram showing the LFP phasebehavior.

DETAILED DESCRIPTION

The present disclosure will now be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown. The particular embodiment(s) is merelyexemplary in nature and is in no way intended to limit the scope of theinvention, its application, or uses, which may, of course, vary. Theinvention is described with relation to the non-limiting definitions andterminology included herein. These definitions and terminology are notdesigned to function as a limitation on the scope or practice of theinvention but are presented for illustrative and descriptive purposesonly. While the processes or compositions are described as an order ofindividual steps or using specific materials, it is appreciated thatsteps or materials may be interchangeable such that the description ofthe invention may include multiple parts or steps arranged in many ways.

As used herein, it will be understood that when an element is referredto as being “on” another element, it can be directly on the otherelement or intervening elements may be present there between. Incontrast, when an element is referred to as being “directly on” anotherelement, there are no intervening elements present.

As used herein, it will be understood that, although the terms “first,”“second,” “third” etc. may be used herein to describe various elements,components, regions, layers, and/or sections, these elements,components, regions, layers, and/or sections should not be limited bythese terms. These terms are only used to distinguish one element,component, region, layer, or section from another element, component,region, layer, or section. Thus, “a first element,” “component,”“region,” “layer,” or “section” discussed below could be termed a second(or other) element, component, region, layer, or section withoutdeparting from the teachings herein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a,” “an,” and “the” are intended to include the pluralforms, including “at least one,” unless the content clearly indicatesotherwise. “Or” means “and/or.” As used herein, the term “and/or”includes any and all combinations of one or more of the associatedlisted items. It will be further understood that the terms “comprises”and/or “comprising,” or “includes” and/or “including” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof. The term “or a combination thereof” or “a mixture of”means a combination including at least one of the foregoing elements.

As used herein, the term about includes additional ranges slightly aboveor below a value without changing the physical characteristics orresultant properties.

As used herein, the single-phase spheniscidite refers to thespheniscidite with less than about 5 weight percent of any additionalphase, such as phosphosiderite or other ammonium iron phosphatecompounds. The single-phase of spheniscidite may be determined using XRDas described in relation to FIG. 6 .

As used herein, the term substantially includes the majority of thesample having the specified property.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Aspects of this disclosure will now be described by example and withreference to the illustrated embodiments listed above. Components,process steps, and other elements that may be substantially the same inone or more embodiments are identified coordinately and are describedwith minimal repetition. It will be noted, however, that elementsidentified coordinately may also differ to some degree.

The present disclosure provides a high-purity ammonium iron phosphatefor use as the primary and/or sole iron phosphate source in thesynthesis of nano-sized lithium iron phosphate (LFP) active primaryparticles for use in cathodes and the methods of making thereof. Theammonium iron phosphate, present as the spheniscidite precursor,provides plate-like particles, as illustrated in FIGS. 1A and 1B. Thismaterial may be used as a precursor for the synthesis of LFP activematerials with a primary particle size of about 100 nm and a surfacearea in a range of 20 m²/g to 25 m²/g. FIG. 4 provides an example methodfor producing the spheniscidite precursor to form a single-phasematerial with a high level of purity as illustrated in FIGS. 5 and 6 .The high purity spheniscidite is then used as a precursor material tosynthesize the LFP active material, an example method provided in FIG. 7, with a high surface area which demonstrates significantly higher powerthan current LFP materials. As illustrated in FIGS. 9 through 21 , theLFP active material synthesized from the spheniscidite precursor for usein a battery, examples illustrated in FIGS. 25 and 26 , providesimproved properties and improved performance at extreme temperatures.

As provided above, a synthesized spheniscidite, also referred to as thespheniscidite precursor, is an ammonium iron phosphate compound with theformula of NH₄Fe₂(PO₄)₂OH*2H₂O as the primary or sole iron phosphatecomponent for the synthesis of the cathode material for use in lithiumion secondary batteries. Spheniscidite has a specific structure thatpossesses two 8-membered channels wherein the ammonium, NH_(4,) and ½ ofthe water molecules reside. The spheniscidite may include from about 35wt. % to about 30 wt. % iron, about 15 wt. % to about 20 wt. %phosphorous, and about 4.6 wt. % to about 5.0 wt. % ammonium, whereinthe use of the term about includes additional ranges slightly above orbelow a value without changing the physical characteristics or resultantproperties. The use of a single-phase and pure spheniscidite as the soleiron phosphate component in the synthesis of LFP provides an LFP activematerial having a small primary particle size and a high surface areaLFP cathode material which surprisingly results in electrochemical cellswith improved electrochemical properties.

One aspect of the present disclosure provides methods for preparingspheniscidite, which is used as a precursor in the LFP synthesis. Insome embodiments, the high-purity spheniscidite has a plate-like shape,as shown in SEMs in FIGS. 1A and 1B and may have less than about 10%total impurities present. With less than 10% total impurities, thematerials may provide the improved properties disclosed herein. Theimpurities may include structural impurities determined from XRD andTGA, as well as, composition impurities, such as Na and/or SO₄impurities, determined from ICP. For example, the pure synthesizedspheniscidite may be free of K and Al, which appear in naturallyoccurring spheniscidite. In other embodiments, the spheniscidite mayhave less than about 5% impurities present. In yet other embodiments,the spheniscidite may have less than about 2.5% impurities present. Ineven other examples, the XRDs indicate no impurity peaks over 2%.

With regards to Na and/or SO₄ impurities, in some examples, there may beless than 2% of such impurities. For example, in an LFP materialsynthesized as disclosed herein, the ICP indicates that the Na and SO4impurities are less than 0.5%.

With regards to further characterizing the spheniscidite, the SEMs showthe resultant spheniscidite has a plate like morphology with the primaryplate particles being about 100 nm along the longest axis of the plate.

Another aspect of the present disclosure provides methods for preparingthe LFP using the synthesized spheniscidite. One embodiment utilizes asolvent based system. Another embodiment utilizes a water based system.The solvent based system may provide particles which include 3Dformations. In some examples, the 3D formations may include, but are notlimited to, spherical shapes. In other examples, the 3D formations mayinclude collapsed spheres or doughnut-like shaped formations. As anotherexample, in the water based system, the particles may be substantiallyspherical.

An LFP is produced which has a primary particle size of about 100 nm,regardless of the solvent system chosen, as illustrated in FIGS. 2A and2B, a surface area in a range of 25 m²/g to 35 m²/g, and a secondary d50particle size in the range of 5 microns to 13 microns, as illustrated inSEMs in FIGS. 3A and 3B. As another example range, the secondary d50particle size may be in the range of about 8 microns to 13 microns. Forexample, the secondary particles may have a d50 particle size of about10 microns.

The methods provided herein include the steps of providing the rawmaterials to obtain pure spheniscidite, providing a lithium source aswell as other reactants to mix with the obtained pure spheniscidite toproduce the final LFP active material with the above mentionedproperties.

Further, the methods include at least one of the steps of mixing,filtering, centrifuging, aging, drying, milling, and heating or acombination thereof.

Furthermore, the methods include the steps of mixing the materials in apre-determined molar ratio and, at specific method steps, controllingthe pH to be within a range of 3-8.5 at one step and controlling the pHto be within a range of about 2 to 4 in a subsequent step.

In an example method, an aqueous ferrous sulfate solution may beoxidized to a ferric ion to produce spheniscidite, as shown in equation1 below. By this example method, an LFP material may be formed by thecombination of spheniscidite and a lithium source material, as shown inequation 2 below. In this example, the lithium source is Li₂CO_(3.) Thespheniscidite and the lithium source are combined to form a LFP activematerial suitable for use in a cathode of a lithium ion cell. A cathodeactive material is thus formed in a two-step reaction, wherein purespheniscidite is produce during reaction 1 for subsequent use as aprecursor material during reaction 2:

Fe(SO₄)*7H₂O+NH₄OH+(NH₄)₂HPO₄+H₃PO₄+H₂O₂|NH₄Fe₂(PO₄)₂OH*2H₂O+H₂SO₄+H₂O  (1)

NH₄Fe₂(PO₄)₂OH*2H₂O+Li₂CO₃|LiFePO₄+H₂O+CO₂+NH₃  (2)

The spheniscidite may be obtained by reacting an iron source, anammonium source, and an oxidant. The spheniscidite obtained has asingle-phase and a high purity. The spheniscidite may have a surfacearea in a range of 20 m²/g to 25 m²/g. For example, in some embodiments,the plate-shaped single-phase spheniscidite precursor may have a surfacearea of about 23 m²/g.

In some embodiments, the iron source compound for making sphenisciditemay be a ferrous salt. The ferrous salt may be hydrated or anhydrous.The ferrous salt, iron (II) salt, may be selected from iron (II)sulfate, iron (II) chloride, iron (II) nitrate, iron (II) oxalate, iron(II) oxide, any hydrate thereof, or a mixture thereof. In one example,iron (II) sulfate heptahydrate, FeSO₄*7H₂O may be used as the ironsource.

In some embodiments, the phosphate source for making spheniscidite maybe selected from H₃PO_(4,) P₂O₅, NH₄H₂PO₄, (NH₄)₂HPO₄, (NH₄)₃PO₄,NaH₂PO₄, Na₂HPO₄, Na₃PO₄, or mixtures thereof. In one example, a mixtureof (NH₄)₂HPO₄ and H₃PO₄ may be used. In another example, (NH₄)₃PO₄ maybe used.

In some embodiments, the ammonium source may be selected from NH₄H₂PO₄,(NH₄)₂HPO₄, (NH₄)₃PO₄, NH₄OH or mixtures thereof. In one example, NH₄OHmay be used.

In some embodiments, an oxidizing agent may be included. The oxidizingagent may be selected from H₂O₂, Na₂O, NaClO₃, or mixtures thereof. Anon-limiting example of an oxidizing agent includes hydrogen peroxide,H₂O₂.

Turning to FIG. 4 , an example method 400 for synthesizing sphenisciditewith a high purity is outlined. For example, the method may include thereactants of reaction 1 above, wherein during reaction 1, the ferrousion, Fe²⁺, is oxidized to the ferric ion, Fe³⁺, to form spheniscidite.In one example, method 400 may include the material processing forreaction 1 including mixing of starting materials, filteringby-products, heating slurry for crystallization, final filtration, andwashing with hot solvent, such as water.

At 402, the method may include mixing the starting materials. Forexample, the iron source, phosphate source, ammonium source, andoxidizing agent are mixed. The starting materials may be mixed atspecific molar ratios. For example, the NH4:PO₄ molar ratio may bebetween about 1.8 to about 3.5, or about 2.0 to about 3.1. In oneexample, the solid starting materials may be dissolved in deionizedwater prior to mixing the starting materials. In another example, thestarting materials may be mixed together in a specific ordering. Asoutlined in reaction 1, one example of mixing the starting materialsincludes mixing FeSO₄*7H₂O, (NH₄)PO₄, H₂O₂, PO4, and NH₄OH. The mixturecomprising the starting materials may have a pH of about 3 to about 8.5.The mixture may be stirred for a time before proceeding to step 404.

At 404, the method may include filtering the by-products. In oneexample, the mixture from 402 may be centrifuged to separate theby-products. In another example, the mixture from 402 may be filterpressed to separate the by-products. The filtering of the by-productsmay be performed multiple times to separate fully the by-products. Forexample, the solution is filtered by centrifuge three times.

At 406, the method may include rinsing the solid obtained duringfiltering at 404. For example, the solid may be rinsed with hotdeionized water. In one example, the solid may be rinsed with hot watermultiple times. In another example, the solid may be continuously rinsedfor a period of time.

At 408, the method may include re-dispersing the rinsed solid from 406.For example, the solid, also referred to as material cakes, may bere-dispersed in deionized water comprising an acid. The solution of there-dispersed solid in deionized water may have a pH controlled to be inthe range of about 1.8 to about 3.1.

At 410, the method may include heating the re-dispersed solid solutionfrom 408. In some examples, the solution may be heated in a selecttemperature range, for example, and not as a limitation, a temperatureat or above 85° C. to at or below 95° C. may be used for a time period.In one example, the entire solution may be heated.

At 412, the method may include filtering the hot solution from 410. Inone example, the solution may be filtered using a filter press. Inanother example, the solution may be filtered using flask filtration.

At 414, the method may include rinsing the solid recovered at 412 withhot deionized water. In one example, the rinsing may be done multipletimes over a period of time. In another example, the rinsing may be donecontinuously over a period to time.

At 416, the method may include drying the rinsed solid from 414. Thesolid may be dried at a temperature which removes any volatile compoundspresent and not desired in the final product.

At 418, the method may include obtaining the spheniscidite. As discussedabove, the spheniscidite may have a high purity wherein less than 10% ofimpurities are present in the spheniscidite, not including ironphosphate materials. For example, the total impurities left in the finalproduct may be less than 10%, and such material may be considered hereinas substantially free of impurities. The level of impurities may bedetermined by ICP, in one example. In other examples, the level ofimpurities in the spheniscidite may be less than 5%. In yet anotherexample, the level of impurities may be less than 2.5%. The method maythen end.

As provided above, a crystalline spheniscidite material, herein alsoreferred to as ammonium iron phosphate material, may be formed. In onenon-limiting example, the crystalline spheniscidite material may includefrom about 25 wt. % to about 30 wt. % iron and from about 15 wt. % toabout 20 wt. % phosphorous, and from about 4.6 wt. % to about 5.0 wt. %ammonium; wherein a molar ratio of phosphorus to iron is from about 1 toabout 1.25. Further, the ammonium iron phosphate may be substantiallyfree of impurities, wherein an XRD may include no impurity peaks over2%. In some examples, the crystalline spheniscidite material may be asingle-phase. Further, in some examples, the crystalline sphenisciditematerial may have a surface area in the range 20 m²/g to 25 m²/g.

A high purity spheniscidite further may be determined by TGA and/or XRDillustrated in FIGS. 5 and 6 respectively. A high purity sphenisciditeproduct may be determined by the substantial absence of any peaks in theXRD or TGA which correspond to iron phosphates materials of morphologiesother than spheniscidite.

Turning to FIG. 5 , a TGA curve 500 of spheniscidite is provided. TheTGA curve 502 has a specific shape for the decomposition of purespheniscidite. The derivative TGA curve shows three peaks 504, 506, and508, which are obtained at specific temperatures. Thus, the TGA curvemay be used to confirm the purity of spheniscidite synthesized, forexample using method 400.

Turning to FIG. 6 , an XRD pattern 600 of spheniscidite is provided. TheXRD curve 602 shows characteristic 2Θ peaks. Thus, the XRD curve may beused to identify phase and purity of the spheniscidite. A single-phaseand high purity spheniscidite is required to produce the final LFPproduct as outlined in the present disclosure below.

The LFP active material for use as a cathode in a battery may beobtained by reacting a high purity spheniscidite, for examplesynthesized as outlined above in method 400, with a lithium source. Thespheniscidite may be the primary or sole iron phosphate source duringthe synthesis of the LFP active material. The synthesis may furtherinclude a dopant and carbon source.

In one embodiment, the high purity spheniscidite may be the primary orsole source of iron phosphate.

In some embodiments, the lithium source may be selected from Li₂CO₃,Li₂O, LiOH, LiF, Lil or mixtures thereof. In one example, the lithiumsource may be Li₂CO₃.

In some embodiments, the dopant, M, may be selected from V, Nb, Ti, AlMn, Co, Ni, Mg, Zr, oxides thereof, or mixtures thereof. The dopant maybe added in amounts up to 10 mol %. In one example, the dopant may bepresent at an amount less than 5 mol %.

In some embodiments, the carbon source may be selected from PVB, citricAcid, sugar, PVA, glycerol or mixtures thereof.

Turning to FIG. 7 , an example method 700 is outlined for the synthesisof LFP from spheniscidite. The final LFP material may be formed bycombining a lithium source and the spheniscidite by mixing, milling, andchemical reduction with a temperature programmed reaction (TPR) underN₂. The resulting LFP active material may then be useable in a cathodeof an electrochemical cell.

At 702, the method may include mixing spheniscidite, a lithium source, adopant, a carbon source, and a solvent to form a slurry. In one example,the solvent may include an alcohol. In another example, the solvent mayinclude water. Thus, the method may include an alcohol or water slurry.The dopant and carbon source may vary based on the solvent choice. Insome examples, more than one carbon source may be included.

In one specific example of reaction (2), the lithium source andspheniscidite may be mixed with a dopant and a carbon source in an IPAslurry. The slurry may then be milled.

At 704, the method may include milling the mixture of 702. The methodmay include milling for a minimum amount of time.

At 706, the method may include drying the milled mixture of 704. Themixture may be dried using a variety of methods known to the industry.

At 708, the method may include firing the dried material of 706. Thematerial may be fired to convert the material to LiFePO₄, LFP, by atemperature programmed reaction (TPR). The TPR may be run in an inertatmosphere, for example N₂. For example, the dried powder may beconverted to LiFePO₄ by TPR in N₂ flow in a tube furnace. The TPRprofile may include ramping from room temperature and then heating. TheTPR may further include programmed holds at specific temperatures.

At 710, the method may obtain the lithium iron phosphate, LFP. Theresulting LFP active materials have a crystalline structure, asillustrated by the XRD pattern provided in FIG. 8 . In addition, thesize of the primary particles, shown in FIGS. 2A and 2B, may be between20 nm to 80 nm, leading to a higher surface area in a range of 25 m²/gto 35 m²/g final LFP active materials, shown in FIGS. 3A and 3B. The useof an alcohol slurry or water slurry results in a similar primaryparticle size in the LFP, as illustrated in FIGS. 2A and 2B. As usedherein, a similar size may be within 5% of one another, for example bysurface area and/or volume. The secondary particle of the LFP differsbased on the solvent slurry. The alcohol slurry secondary particle shapeis shown in FIG. 3A and the water slurry secondary particle shape isshown in FIG. 3B. The alcohol slurry secondary particle shape shows avariety of shapes while the water slurry secondary shape shows spheresthat are more exact.

Turning to FIG. 8 , an XRD pattern 800 of the LFP is shown. The XRDcurve 802 may be used to determine the purity of the resultant LFP. TheXRD curve 802 shows characteristic 20 peaks, indicating a purecrystalline LFP. Thus, the XRD curve may be used to identify phase andpurity of the LFP. A high purity spheniscidite is required to producethe final crystalline LFP product as outlined in the present disclosurewherein the final crystalline LFP product improves battery performanceat low temperatures. For example, the LFP product may improve batteryperformance at 0° C. or lower. In another example, the LFP product mayimprove battery performance at low temperatures of −20° C. down to −30°C.

A resulting LFP active material can be tested in a non-aqueouselectrochemical cell. The LFP active material serves as the positiveelectrode against a source of lithium having a total lithium contentmuch greater than the lithium storage capacity of the LFP electrode,such as lithium foil. This electrochemical cell construction is oftenreferred to as a lithium half-cell by those skilled in the art oflithium-ion batteries. In such a cell, the LFP active material isformulated into an electrode, optionally using a conductive additive,such as carbon, and a polymeric binder. The LFP active materialelectrode is separated from the lithium metal counter electrode,optionally by a microporous polymer separator. The cell is then infusedwith a nonaqueous lithium-conducting liquid electrolyte. The charge anddischarge rates of the electrode are sufficiently fast that theelectrochemical behavior of the LFP electrode material can be tested.

As such, an LFP active material is optionally used in an electrochemicalcell as a component of either a cathode or an anode, although a cathodeis typical. An electrochemical cell includes an LFP active materialcontaining electrode and a counter electrode. A counter electrodeincludes an anode base material. In some embodiments, an anode basematerial optionally includes silicon, graphitic carbon, silicon carboncomposites, tin, Ge, Sb, AI, Bi, As, Li metal, lithium alloys, metalalloys, transition metal oxides, nitride materials, sulfide materials,and combinations thereof. An alloy optionally includes one or more ofMg, Fe, Co, Ni, Ti, Mo, and W.

Illustrative examples of a metal alloy for use as an anode base materialinclude silicon alloys. A silicon alloy is optionally and alloy ofsilicon and Ge, Be, Ag, AI, Au, Cd, Ga, In, Sb, Sn, Zn, or combinationsthereof. The ratio of the alloying metal(s) to silicon is optionally 5%to 2000% by weight, optionally 5% to 500% by weight, optionally 20% to60% by weight, based on silicon.

In some embodiments, an anode base material includes a lithium alloy. Alithium alloy optionally includes any metal or alloy that alloys withlithium, illustratively including Al, Si, Sn, Ag, Bi, Mg, Zn, In, Ge,Pb, Pd, Pt, Sb, Ti, tin alloys, and silicon alloys.

Additional examples of alloys and methods of alloy production can befound in U.S. Pat. No. 6,235,427, herein incorporated by reference forall purposes. In some embodiments, the anode base material is orincludes: silicon; carbon and graphitic carbon materials such as naturalgraphite, graphene, artificial graphite, expanded graphite, carbonfibers, hard carbon, carbon black, carbon nanotubes, fullerenes andactivated carbon; a composite material of a metal or metal compound anda carbon or graphite material whereby a metal optionally includeslithium and silicon; and a lithium-containing nitride. As such, theanode base material, also referred to here as the negative electrode,may include non-graphitizable carbon, artificial graphite, and naturalgraphite combinations of carbonaceous materials with silicon or siliconoxide.

Optionally, an electrode base material is not graphite alone in theabsence of silicon, lithium, or a metal. In some embodiments, an anodebase material is a composite material of silicon and graphitic carbonthat may or may not include a carbon coating and or thermal treatment tostabilize the adhesion of the coating to the surface. In someembodiments, an anode base material includes a coating, illustratively acarbon coating.

An anode base material or an LFP active material may or may not beassociated with a conductive substrate. When associated with asubstrate, the substrate is optionally formed of any suitableelectronically conductive and impermeable or substantially impermeablematerial, including, but not limited to, copper, stainless steel,titanium, or carbon papers/films, a nonperforated metal foil, aluminumfoil, cladding material including nickel and aluminum, cladding materialincluding copper and aluminum, nickel plated steel, nickel platedcopper, nickel plated aluminum, gold, silver, any other suitableelectronically conductive and impermeable material or any suitablecombination thereof. In some embodiments, substrates may be formed ofone or more suitable metals or combination of metals (e.g., alloys,solid solutions, plated metals). Optionally, an anode base material orLFP active material is not associated with a substrate.

In some embodiments, the inventive LFP active material may be used in anelectrode for a secondary battery. An electrode is optionally fabricatedby suspending a LFP active material and a binder (optionally at 1-10% byweight of solvent) in a solvent to prepare a slurry, and applying theresulting slurry to a current collector, followed by drying andoptionally pressing. Exemplary binders include PVDF binder solutions inNMP or aqueous polyolefin latex suspensions. Examples of the solventused in preparation of the electrode may include, but are not limited tocarbonate-based, ester-based, ether-based, ketone-based, alcohol-based,or aprotic solvents. Specific organic solvents such as dimethylsulfoxide (DMSO), N-methyl pyrrolidone (NMP) and ethylene glycol, anddistilled water may be used. Such solvents are known in the art.

An electrochemical cell is also provided that uses an electrode formedof an LFP active material substantially as provided by the applicationwith embodiments as described herein. The electrochemical cellsoptionally employ a porous electronically insulating separator betweenthe positive and negative electrode materials, and a liquid, gel orsolid polymer electrolyte. The electrochemical cells optionally haveelectrode formulations and physical designs and constructions that aredeveloped through methods well-known to those skilled in the art toprovide low cell impedance, so that the high power capability of the LFPactive material may be utilized.

Optionally, the LFP active materials described herein typically containless than about 5 weight percent, or about 3 weight percent, of anyadditional phase that does not substantially store ions, but may provideadded electrical conductivity. Such additional phases include, forexample, carbon, a metal, or an intermetallic phase, such as a metalphosphide, metal carbide, metal nitride, or mixed intermetalliccompound, such as metal carbide-nitride or metal carbide-phosphide. Theelectrode materials may include an amount of carbon in the range of 2.1%to 2.5%. In some examples, the primary and secondary particles of theLFP may have a carbon percentage of about 2.3%.

In certain embodiments, for use as a storage electrode, the LFP activematerial typically is formulated into an electrode by standard methods,including the addition of a few weight percent of a polymeric binder,and less than about 10 weight percent of a conductive additive, such ascarbon. In at least some such embodiments, the electrodes are coatedonto one or both sides of a metal foil (e.g. substrate), and optionallypressed to a coating thickness of between about 30 micrometers and about200 micrometers. Such electrodes can be used as the positive or negativeelectrode in a storage battery. Their performance can be evaluated, forexample, using laboratory cells of the coin-cell or so-called Swagelokcell types, in which a single layer of electrode is tested against acounter electrode (typically lithium metal when the nanoscale materialis a lithium storage material) using galvanostatic (constant current) orpotentiostatic (constant voltage) tests or some combination of the two.Under galvanostatic conditions, the current rate can be described as“C-rate,” in which the rate is C/h, and n is the number of hoursrequired for substantially complete charge or discharge of the cellbetween a selected upper and lower voltage limit.

An electrochemical cell includes an electrolyte. An electrolyte isoptionally a solid or fluid electrolyte. Illustratively, the electrolyteincludes a lithium salt and a non-aqueous organic solvent. A lithiumsalt is optionally LiPF₆, LiBF₄, LiSbF₆, LiAsF₆, LiN(SO₂C₂F₅)₂,Li(CF₃SO₂)₂N, LiFSI, LiTFSI, LiN(SO₃C₂F₅)₂, LiC₄F₉SO₃, LiClO₄, LiAlO₂,LiAlCl₄, LiCl, LiI, or LiB(C₂O₄)₂ (lithium bis(oxalato)borate; LiBOB).The lithium salt is optionally present in a concentration ranging fromabout 0.1 M to about 2.0 M. When the lithium salt is included at theabove concentration range, an electrolyte may have excellent performanceand lithium ion mobility due to optimal electrolyte conductivity andviscosity.

Thus, as described above, in some examples, a method, is providedincluding introducing an iron (II) salt, a phosphate source, an ammoniumsource, and an oxidizing agent into an aqueous solution to form amixture. The mixture may be filtered to recover a solid by-product andthen the solid by-product may be re-dispersed into an aqueous solution.The aqueous solution may be heated and then filtered to recover a solid.The solid may be dried to obtain a high purity spheniscidite with aformula of NH₄Fe₂(PO₄)₂OH*2H₂O. The high purity spheniscidite may be asingle-phase.

In some examples, the iron (II) salt may be selected from iron (II)sulfate, iron (II) chloride, iron (II) nitrate, any hydrate thereof, ora mixture thereof. Further, in some examples, the phosphate source maybe selected from H₃PO₄, P₂O₅, NH₄H₂PO₄, (NH₄)₂HPO₄, (NH₄)₃PO₄, NaH₂PO₄,Na₂HPO₄, Na₃PO₄, or mixtures thereof. Moreover, in some examples, theammonium source may be selected from NH₄H₂PO₄, (NH₄)₂HPO₄, (NH₄)₃PO₄,NH₄OH or mixtures thereof. The oxidizing agent also may be selected fromH₂O₂, Na₂O, NaClO₃, or mixtures thereof.

As another example, the method may further include mixing the obtainedhigh purity spheniscidite, a lithium source, a dopant, and a carbonsource, adding a solvent to produce a slurry, milling the slurry, dryingthe milled slurry, and firing the dried milled slurry to obtain thelithium iron phosphate, wherein the lithium iron phosphate comprises asubstantially olivine crystalline phase, a primary particle in the rangeof 20 nm to 80 nm, a secondary particle with a d50 in the range of 5 μmto 13 μm, and a surface area of 25 m²/g to 35 m²/g, a carbon percentageof about 2.3%. The lithium iron phosphate may be substantially in anolivine crystalline phase where there may be less than 5 weight percentof any additional phases which do not substantially store ions. Thelithium iron phosphate may improve battery performance at lowtemperatures in comparison to current lithium iron phosphate materials.For example, the current lithium iron phosphate materials may bestoichiometric lithium iron phosphate materials, wherein the elementsare present in the ratios prescribed by the formula LiFePO₄.

In some examples, with milling, primary particles may be obtained ofabout 20 nm to about 80 nm. It should be appreciated that the method mayinclude a solvent where the solvent is water and/or a compound includingan alcohol functional group.

In one example, a lithium iron phosphate (LFP) is provided comprisingcrystalline primary particles and secondary particles, wherein theprimary particles are formed from a plate-shaped single-phase ammoniumiron phosphate spheniscidite precursor and a lithium source. The LFP,herein also referred to as a spheniscidite-derived LFP, may be formedfrom the spheniscidite precursor and show a specific LFP phase behavior.The spheniscidite-derived LFP may exhibit different phase behavior thana conventional LFP, even when the conventional LFP has similarcharacteristics (for example primary particle size, specific surfacearea, or similar XRD peak broadening).

For example, as illustrated in FIG. 29 , an example phase diagram forthe LFP illustrates the extended solid-solution range of the LFP incomparison to the conventional LFP of similar physical characteristics,e.g. particle size and/or specific surface area, for example an LFP ofsimilar physical characteristics but without pure ammonium ironphosphate spheniscidite precursor. In one example, the similarcharacteristics may be a similar size within 5% of one another and/orwithin 5-10% of surface areas of one another. The LFP phase behavior mayinclude an extended solid-solution range, which may be due to the use ofthe pure ammonium iron phosphate spheniscidite precursor. The LFP phasebehavior, including the extended solid-solution range of the LFP, maytranslate to improved battery properties, for example when used inlithium ion cells. For example, the LFP may show improved temperatureperformance, such as at low temperature, and improved capacity. Inaddition, the two-phase field may occur over a smaller range of Liconcentration for the LFP at the same temperature in comparison toconventional LFP materials having similar particle sizes. This iscontrary to the conventional way of thinking where the two-phase fieldshrinks with decreasing particle size, and has the same behavior for thesame particle sizes. The LFP may also show extended solid-solutionranges in comparison to conventional LFP's of similar size over a rangeof temperatures.

For example, 2900 and 2904 of FIG. 29 show voltage versus dischargecapacity curves at a discharge rate of 10 C (current density todischarge the full capacity of the battery device in 1/10 of an hour)for the LFP 2902, which illustrates the extended solid-solution range ofthe LFP, in comparison to the conventional LFP 2906. The LFP and theconventional LFP have similar physical characteristics, e.g. particlesize and/or specific surface area. The similar characteristics may be asimilar size within 5% of one another and/or within 5-10% of surfaceareas of one another. The shapes of the two discharge curves illustratethat the LFP material 2902 provides an improved battery material forhigh-rate applications as compared to the conventional LFP 2906. Theshape of the discharge curves at the last 25% of the discharge showclear differences as the voltage begins to decrease. The LFP 2902 curveshows a sharper, defined change in slope, occurring just above 3V. Thedischarge curve shape of the LFP 2902 may illustrate the change in themode of lithium intercalation within the active material particles. Morespecifically, illustrated by the flatter portion of the discharge curve,the LFP material may be lithiated via a two-phase reaction, where twodistinct crystalline phases co-exist (i.e. the LFP phase behavior). Afirst phase may be present in a predominately lithiated state and asecond phase may be present in a predominately unlithiated state.However, in some materials, a one-phase lithiation reaction may occur,which may also enhance faster lithium intercalation kinetics. Thepercentage of the total lithiation reaction occurring in a two-phaseversus a one-phase lithiation reaction may control the overall rateperformance of the active cathode material.

In contrast to the LFP 2902, the conventional LFP 2906 shows adistinctly different discharge voltage curve. The overall voltage of thebattery employing the conventional LFP is lower in comparison to the LFP2902. Further, the discharge curve of the conventional LFP 2906 is morecurved and continuously rounded, especially during the last 25% of thedischarge. The conventional LFP 2906 does not show a sharp transitionbetween the two nearly linear sloping regions. The characteristics ofthe conventional LFP 2906 show a material with higher overall netimpedance. The impedance may limit a battery from completely dischargingall its capacity, as illustrated by the shorter capacity at the end ofdischarge at 2V for the conventional LFP 2906. The smoothly slopingnature of the discharge curve of the conventional LFP 2906 does notillustrate a clear transition from a two-phase to a single phaselithiation reaction, as is seen the LFP 2902. For example, highresolution X-ray diffraction of the LFP and the conventional LFP atvarious states of discharge would illustrate the differences in thephase behavior and the lithiation mechanism. FIG. 29 illustrates thatthe LFP 2902, prepared from pure ammonium iron phosphate sphenisciditeprecursor, has an improved rate performance in comparison to theconventional LFP 2906. Further, the LFP may be concluded to have a modeof lithiation, more specifically a phase change behavior when the LFP issufficiently discharged, which is different from the conventional LFP.Thus, the LFP may include an LFP phase behavior.

The differences in shape of the discharge capacity curves, as describedabove and illustrated in 2900 and 2904 for the LFP 2902 and theconventional LFP 2906, may indicate that the LFP has less polarizationthan the conventional LFP. The conventional LFP 2906 discharge curvedoes not show a clear break in the two slope areas, indicating that thebehavior may be controlled by polarization, whereas the LFP 2902discharge curve shows a more clear break in the two slope areas,indicating that the behavior has less polarization. For example,polarization in an electrochemical process may lower the efficiency ofthe process. The lower polarization and clear breaks in the two-slopeareas may indicate the presence of a wider solid-solution range in thespheniscidite-derived LFP.

In one embodiment, the LFP phase behavior may exhibit characteristicssuch as an extended solid-solution range. For example, thespheniscidite-derived LFP may possess different phase behavior fromstandard materials, including, but not limited to, extendedsolid-solution ranges at the same temperature and particle size. Theextended solid-solution range in the LFP may be greater at the sametemperature and particle size in comparison to current LFP materials. Asyet another example, the lithium iron phosphate may exhibit an LFP phasebehavior wherein the LFP phase behavior includes, as a non-limitingexample, an extended solid solution range where x in Li_(x)FePO₄ exceeds0.2 at Li-poor compositions, and is less than 0.8 at Li-richcompositions, at 45° C. for a primary particle size of 20 nm-80 nm. Inyet another non-limiting example, an extended solid solution range wherex in Li_(x)FePO₄ exceeds 0.1 at Li-poor compositions, and is less than0.15 at Li-rich compositions, at 0° C. for a primary particle size of 20nm-80 nm may be seen for the LFP.

In a non-limiting example, the LFP phase behavior may provide extendedsolid-solutions in a wider range of lithium compositions over which asolid-solution occurs. For example, in some embodiments, the LFP phasebehavior may be such that the difference in the solid-solution ranges isa wider range of Li composition over which a solid solution occurs atlow or at high states of charge (or high and low overall Liconcentration).

The modifications of the LFP phase behavior may provide for improvedbattery performance at a variety of temperatures, for example lowtemperatures, and improved capacity in comparison to current lithiumiron phosphate materials. Thus, the use of the pure ammonium ironphosphate spheniscidite precursor may be to provide a precursor materialwhich introduces an LFP phase behavior into the synthesized lithium ironphosphate material, resulting in improved performance in batteryapplications. Specifically, for example, the modified LFP phase behaviormay result in extended solid-solution ranges in the lithium ironphosphate. This LFP phase behavior is an unexpected result when comparedto other LFP materials having similar specific surface area, particlesize, or exhibiting similar x-ray diffraction peak broadening. This isat least partially due to the fact that spheniscidite-derived LFPexhibits different phase behavior in comparison to a conventional LFPmaterial of the same BET specific surface area (or primary particlesize, or exhibiting the same X-ray peak broadening).

In a non-limiting example, the markedly superior power at lowtemperature of battery cells having the spheniscidite-derived LFP may beobtained despite this material having a lower BET specific surface areaand less X-ray peak broadening. Therefore, in this example, larger LFPprimary crystallite size does not result in an inferior performance, dueto the LFP phase behavior.

Further, the LFP phase behavior and improved performance characteristicsappear not to be due to a shorter diffusion distance at the crystallitelevel. Also, unexpectedly, the performance may not be explained by thepresence of conductive impurity phases since the amount of those phasescan be widely varied with composition, heat treatment temperature, andfiring atmosphere, and have not previously resulted in the exceptionallow temperature behavior of the disclosed LFP.

It is also considered that olivine cathode materials may suppress thetwo-phase immiscibility field inherent to LFP and thereby avoid thefirst order phase transition. Published scientific literature on olivinecathode materials indicate that suppressing the two-phase immiscibilityfield inherent to LFP, and thereby avoiding the first-order phasetransition and its associated high mechanical strain, may be responsiblefor obtaining high power. Without being bound by any particularscientific interpretation, the range of Li concentration over whichimmiscible solid phases of differing Li concentration appear, at anygiven temperature, may be decreased by creating defects and atomicdisorder. Further, since the immiscibility field in pure LixFePO₄ isrelatively symmetric in composition space between Li concentrations ofzero and one, the effects of diminished immiscibility may generally beseen at low and high Li concentrations, corresponding to high and lowstates of charge of the corresponding battery cell.

As a comparative example, in undoped nanoparticulate LFP, it has beenfound that the extent of solid solution at low overall Li concentrationsis lower than 20% at an equivalent spherical particle size obtained fromthe BET specific surface area of 34 nm, is lower than 10% at a particlesize of 42 nm, and is lower than 5% at a particle size of 100 nm. Incontrast to the comparative LFP examples, the unexpected LFP phasebehavior of the spheniscidite-derived material has an increased extendedsolid-solution range at the same temperature and particle size incontrast to prior LFP materials.

As a non limiting example, the LFP phase behavior of thespheniscidite-derived material may include a lithium amount in solidsolution that is greater than or less than 20% of a stoichiometriclithium iron phosphate of the same particle size. In another example,the phase behavior includes a lithium amount in solid solution that isgreater than or less than 5% of a stoichiometric lithium iron phosphateof the same particle size. The lithium iron phosphate may show a lithiumnonstoichiometry, i.e. an extended solid-solution range. The lithiumiron phosphate extended solid-solution allows for the crystallinestructure, in which lithium may be delithiated or lithiated, to remainthe same. Thus, the LFP phase behavior of the LFP shows a homogeneoussolid that may exist over a wider range of lithiation and delithiation(i.e. lithium amount) in comparison to conventional LFP material notsynthesized using a pure ammonium iron phosphate sphenisciditeprecursor. The LFP phase behavior of the LFP shows an unexpectedly widerange where the solid-solution exists as compared with the conventionalLFP's sharing similar physical characteristics.

As another example, the phase behavior may show a two-phase fieldwherein x may be 0.2<x<0.8 for Li_(x)FePO₄ at a temperature of about 45°C. and the extended solid-solution range occurs outside of the two-phasefield range.

In some embodiments, the spheniscidite-derived LFP may include one ormore structural differences from prior LFPs. These structuraldifferences may include subtle morphology differences or differences incrystal lattice dimensions, which may produce differences in latticestrain at high and low lithium occupancy. Such structural differencesmay enable an unexpected and dramatic difference in lithiation, such aswhere the overall crystallite/grain dimensions and resulting lithiumdiffusion lengths are similar. The mechanistic and possibly structuraldifferentiation of the disclosed LFP material may result in startlingand dramatic difference in rate performance.

As another example embodiment, the spheniscidite-derived LFP furtherprovides an improvement in the rate of lithium insertion/extraction. Asa non-limiting example, the LFP phase behavior of thespheniscidite-derived material may result in the rate of lithiuminsertion/extraction being improved, e.g. at a rate of 20 C, 90%discharge capacity is retained compared to C/10. Despite having similarcrystalline dimensions of 20-80 nm of the LFP, a comparative material iscapable of only 80% discharge capacity at 20 C being retained.

Further, impurities may be present on the M1 site in an olivine lithiumiron phosphate, where the M1 site is the lithium site in the olivinestructure. Minimizing the amount of impurities on the M1 site mayimprove battery performance, such as with the disclosed LFP. Forexample, the spheniscidite-derived LFP may minimize the amount ofnon-lithium atoms, i.e. impurities, on the M1 site in comparison to LFPsnot synthesized using spheniscidite. In one example, the impurities onthe M1 site may be less than about 5%. In another example, theimpurities on the M1 site may be less than about 1% of the sites.

In order to further support the disclosure, various aspects of thepresent application are illustrated by the following non-limitingexamples. The examples are for illustrative purposes and are not alimitation on any practice of the present application. Reagentsillustrated herein are commercially available, and a person of ordinaryskill in the art readily understands where such reagents may beobtained.

EXPERIMENTAL

A spheniscidite material is formed as per reaction 1 wherein the methodmay include the ferrous ion, Fe²⁺, oxidized to the ferric ion, Fe³⁺, toform spheniscidite. The resulting spheniscidite has the followingproperties listed in Table 1:

TABLE 1 pH pH NH₄:P NH₄OH 1^(st) 2^(nd) Morphology ratio (g) step stepP/Fe Color Texture FCC C/5 10C C % N % BET Spheniscidite/trace 2.01415.00 2.96 2.04 1.2 Yellow Soft 154 163 149 2.67 0.30 30.8Phosphosiderite Spheniscidite 2.137 22.58 3.09 2.20 1.02 Yellow Soft 158169 154 2.48 0.20 29.8

The various spheniscidite materials are tested by ICP-AES with thefollowing results listed in Table 2:

TABLE 2 Synthesis ICP Results of Product pH 1^(st) pH 2^(nd) Fe- Na- S-Morphology Description step step wt % P P/Fe wt % wt % Spheniscidite0.373 mol NH₄ ⁺ in 3.09 2.20 29.2 16.44 1.02 0.002 0.271 DAP (2.14 mlratio NH₄:PO₄), age 2/3 t = 2 hr, 10 min filter (yellow) Spheniscidite +0.250 mol NH₄ ⁺ in 2.96 2.04 29.03 16.42 1.02 0.002 0.323phosphosiderite DAP (2.01 mol (trace) ratio NH₄:PO₄), age 2/3 t = 2 hr,10 min filter (yellow) Spheniscidite + 0.210 mol NH₄ ⁺ in 2.94 2.0427.64 16.36 1.07 0.003 1.113 phosphosiderite DAP (1.97 mol (trace) ratioNH₄:PO₄), age 2/3 t = 2 hr, 55 min filter (yellow)

In one example, a conductive additive may be added to the sphenisciditealong with a metal oxide dopant, and a carbon additive. The mixture maybe mixed with a solvent, for example, an alcohol based solvent to form aslurry. The slurry may then be milled. The milled slurry may then bedried and sieved. The dried powder may be fired to convert the materialinto the final LFP product.

In another example, a conductive additive may be added to thespheniscidite, along with a metal salt dopant, at least one carbonadditive, followed by mixing in a water solvent slurry. In someexamples, more than one carbon additive may be used. The slurry may thenbe milled. The milled slurry may then be dried. The dried slurry maythen be fired to convert the material into the final LFP product.

The resulting LFP active material is used to form a Swagelok electrodethat includes 79% active material, 10% carbon, and 11% binder mass ratioto make a loading of 0.45-0.49 mAhr/cm². The Swagelok half-cells arecharged at C/2 to 3.8V CCCV and discharged with CC to 2 V with differentC-rates. The discharge charge storage capacities at different C-rateswere measured, and the rate-capability calculated. In some examples, therate-capability at 10 C is greater than 130 mAh/g in a Swagelokhalf-cell.

Process 1

Swagelok FCC C/5 10 C Energy (RT) 488.9 516.0 441.1 Energy (0° C.) 486.8497.1 318.8

Process 2

Swagelok FCC C/5 10 C Energy (RT) 502.2 510.3 437.2 Energy (0° C.) 506.8488.8 291.8

Turning to FIGS. 9 through 24 , the performance of an electrochemicalcell comprising the LFP synthesized from pure spheniscidite isillustrated in comparison to an electrochemical cell comprising currentLFP materials. The electrochemical cell comprises a cathode, an anode,an electrolyte, and a separator. As used herein, the anode, theseparator, and the electrolyte in the electrochemical cell were the samefor a given test.

Turning to FIG. 9 , the first charge capacity of the LFP material usedin a cathode is illustrated. The first charge capacity of the LFP 902synthesized from pure spheniscidite is improved over current LFPmaterials 904 and 906 used in cathodes in Li-ion cells.

Turning to FIG. 10 , the first discharge capacity of the LFP materialused in a cathode is illustrated. The first discharge capacity of theLFP 1002 synthesized from pure spheniscidite is improved over currentLFP materials 1004 and 1006 used in cathodes in Li-ion cells.

Turning to FIG. 11 , a percentage of first charge capacity of the LFPsynthesized from spheniscidite is compared to current LFP materials. TheLFP 1102 synthesized from spheniscidite shows percentage of first chargecapacity similar to current LFP 1104 and slightly lower than current LFP1106

Turning to FIG. 12 , an absolute capacity loss of the LFP synthesizedfrom spheniscidite is compared to current LFP materials. The LFP 1202synthesized from spheniscidite shows a lower absolute capacity losscompared to the current LFP 1204 and 1206 materials.

Turning to FIG. 13 , an alternating current resistance (ACR) impedancefor cells with the LFP material used in a cathode is illustrated.Compared to the current LFP materials 1304 and 1306, the LFP 1302synthesized from spheniscidite shows improved ACR impedance.

Turning to FIG. 14 , a direct current resistance (DCR) impedance forcells with the LFP material used in a cathode is illustrated. Comparedto the current LFP materials 1404 and 1406, the LFP 1402 synthesizedfrom spheniscidite shows improved DCR impedance.

Turning to FIG. 15 , the capacity retention after 3 days of aging isshown for the LFP material used in a cathode is illustrated. The LFP1502 synthesized from spheniscidite shows a similar capacity retentionin comparison to the current LFP materials 1504 and 1506.

Turning to FIG. 16 , the electrode thickness after calendaring andformation is illustrated. The average cathode 1604 and anode 1608thickness after calendering and the average cathode 1602 and anode 1606thickness after formation show values that indicate acceptable swellingof the electrode comprising the LFP synthesized from spheniscidite.

Turning to FIG. 17 , the hybrid pulse power characterization (HPPC) DCRimpedance at 1 s and 20 s for the LFP material used in a cathode isillustrated at 23° C. The 1 s DCR results are illustrated for the LFP1702 synthesized from spheniscidite and the current LFP 1704 and 1706materials and the 20 s DCR results are illustrated for the LFP 1708synthesized from spheniscidite and the current LFP 1710 and 1712materials. The LFP 1702 and 1708 shows reduced DCR at both the 1 s and20 s DCR.

Turning to FIG. 18 , the hybrid pulse power characterization (HPPC) DCRimpedance at 10 s of the LFP material used in a cathode is illustratedat 23° C. The 10 s DCR shows results similar to the 1 s and 20 s resultsillustrated in FIG. 17 above. The LFP 1802 synthesized fromspheniscidite shows reduced DCR compared to the current LFP 1804 and1806 materials.

Turning to FIG. 19 , the hybrid pulse power characterization (HPPC) at−20° C. at 1 s and 20 s pulse power for the LFP synthesized fromspheniscidite. The 1 s DCR results are illustrated for the LFP 1902synthesized from spheniscidite and the current LFP 1904 and 1906materials and the 20 s DCR results are illustrated for the LFP 1908synthesized from spheniscidite and the current LFP 1910 and 1912materials. The LFP 1902 and 1908 shows reduced DCR at both the 1 s and20 s DCR and shows 40% improvement at is and 20% improvement at 20 s ata 50% SOC at low temperature.

Thus, the disclosed electrode material, the LFP synthesized fromspheniscidite, has at least a 10% improvement in direct currentresistance pulse discharge at −20° C. as compared to a control electrodematerial not formed from the plate-shaped single-phase sphenisciditeprecursor wherein the electrochemical cell components are the same. Asdiscussed previously, the electrochemical cells prepared for testing mayinclude the same components, such as the anode, separator, electrolyte,in order to provide a comparison between the cathode electrodematerials.

Turning to FIG. 20 , the double layer pouch cell (DLP) with 0.5×electrode loading and 5 C for 30 secat 50% SOC is shown. In theparticular DLP illustrated, the LFP synthesized from spheniscidite showsa 45% improvement in average DCR as compared to the current LFP materialand provides less than 9 ohms impedance at 50% SOC. The LFP synthesizedfrom spheniscidite shows improved cold temperature performance.

Turning to FIG. 21 , the voltage profile for a 10 C discharge to 100%depth of discharge (DOD for the LFP synthesized from spheniscidite isshown. The voltage profile 2002 illustrates that the LFP synthesizedfrom spheniscidite and shows an improvement in energy as compared to thecurrent LFP 2004 material.

Turning to FIG. 22 , the normalized rate capability at various dischargerates of the LFP synthesized from spheniscidite compared to current LFPmaterials is shown. The LFP 2102 shows increased rate capabilitycompared to current LFP materials 2106 and 2104.

Turning to FIG. 23 , the direct current resistance pulse discharge at−30° C. at 10 s for the LFP synthesized from spheniscidite compared tocurrent LFP materials is shown. The LFP 2202 synthesized fromspheniscidite shows about a 20% decrease in DCR and 40% increase inpower (refer to 2208) as compared to current LFP 2204 and a largerimprovement over current LFP 2206.

Turning to FIG. 24 , the power resulting from a cold crank test at −30°C. over time, measured in seconds, for the LFP synthesized fromspheniscidite compared to current LFP materials is shown. The LFP 2302synthesized from spheniscidite shows increased power as compared to thecurrent LFP 2304 and 2306 materials over time measured in seconds.

Turning to FIG. 25 , the alternating current impedance for the LFPsynthesized from spheniscidite compared to current LFP materials isshown. The LFP 2402 synthesized from spheniscidite shows the lowestcharge transfer resistance. The current LFP 2404 and 2406 materials showhigher charge transfer resistance.

The embodiments described above may be used in prismatic and cylindricalelectrochemical cells. For purposes of this document, a prismatic cellis defined as a cell having a rectangular profile within a planeperpendicular to the length of the cell. Prismatic cells should bedistinguished from round (cylindrical) cells that have a circularprofile within this plane.

Turning to FIG. 26 , an electrode assembly is illustrated which mayinclude the disclosed LFP electro-active material. The LFP activematerial synthesized from spheniscidite may be present as a cathode oranode. In a stackable cell configuration, multiple cathodes and anodesmay be arranged as parallel alternating layers. In the exampleillustrated in FIG. 25 , a stackable cell electrode assembly 2500 isshown. The electrode assembly 2500 is shown to include seven cathodes2502 a-2502 g and six anodes 2504 a-2504 f. In one example, the cathodesmay comprise the LFP synthesized from spheniscidite as described above.In another example, the anodes may comprise the LFP synthesized fromspheniscidite. Adjacent cathodes and anodes are separated by separatorsheets 2506 to electrically insulate the adjacent electrodes whileproviding ionic communication between these electrodes. Each electrodemay include a conductive substrate (e.g. metal foil) and one or twoactive material layers supported by the conductive substrate. Eachnegative active material layer is paired with one positive activematerial layer. In the example presented in FIG. 25 , outer cathodes2502 a and 2502 g include only one positive active material facingtowards the center of assembly 2500. One having ordinary skill in theart would understand that any number of electrodes and pairing ofelectrodes may be used. Conductive tabs may be used to provideelectronic communication between electrodes and conductive elements, forexample. In some examples, each electrode in electrode assembly 2500 mayhave its own tab. Specifically, cathodes 2502 a-2502 g are shown to havepositive tabs, 2510 while anodes 2504 a-2504 f are shown to havenegative tabs.

In FIGS. 27A and 27B, a wound cell example 2600 is illustrated in whichtwo electrodes are wound into a jelly roll and housed within acontainer. The container housing the negative electrode, the positiveelectrode, the nonaqueous electrolyte and the separator.

The LFP synthesized from pure spheniscidite having primary particles inthe range of 20 nm to 80 nm and a surface area in a range of 25 m²/g to35 m²/g shows improved properties when used as an electroactive materialin a battery. In one example, the surface area of the LFP synthesizedfrom pure spheniscidite may be about 30 m²/g. The LFP shows reduced DCR,about 50% as illustrated in the HPPC data above, an increased power byabout 40% during cold cranking, an increased rate capacity retention,and lowered charge transfer resistance.

Turning to FIG. 28 , a XRD shows diffraction data illustrating that thesynthesized LFP 2802 has a crystallite size within the range of currentLFP crystallite sizes 2804 and 2806, as indicated by the full width athalf maximum of the peaks. As the synthesized LFP shows improved batteryperformance in lithium ion cells, the synthesized LFP may have amodified LFP phase behavior. For example, the LFP phase behavior of thesynthesized LFP may include the extended solid solution range, whereinthe extended solid solution range has a composition Li_(x)FePO₄, where xexceeds 0.2 at Li-poor compositions and is less than 0.8 at Li-richcompositions, at about 45° C.; and wherein the primary particles have aparticle size in the range of 20 nm to 80 nm. In yet another example,the extended solid solution range has a composition Li_(x)FePO₄, where xexceeds 0.1 at Li-poor compositions, and is less than 0.15 at Li-richcompositions, at 0° C. for a primary particle size of 20 nm-80 nm may beseen for the LFP. Thus, the solid-solution range of the LFP having aprimary particle size of 20-80 nm, wherein the particle size iscomparable to current, stoichiometric, LFP materials, is extended.However, current LFP materials do not show the same improved batteryperformance, for example at low temperatures, and therefore do notpresent a similar phase behavior as the spheniscidite-derived LFP. TheLFP phase behavior may be unique to the synthesized LFP as the LFP isprepared using a pure ammonium iron phosphate spheniscidite precursor,which is not present in current LFP materials.

Thus, the current disclosure provides an LFP material with specificcharacteristics synthesized from a pure spheniscidite, used as theprimary or sole iron phosphate source, which surprisingly improvesbattery performance. The LFP material may be synthesized as describedabove from a plate-shaped single-phase ammonium iron phosphate precursorand a lithium source such that it exhibits a different solid phasebehavior, specifically an extended solid-solution range as describedabove.

Various modifications of the present invention, in addition to thoseshown and described herein, will be apparent to those skilled in the artof the above description. Such modifications are also intended to fallwithin the scope of the appended claims.

It is appreciated that all reagents are obtainable by sources known inthe art unless otherwise specified.

Patents, publications, and applications mentioned in the specificationare indicative of the levels of those skilled in the art to which theinvention pertains. These patents, publications, and applications areincorporated herein by reference to the same extent as if eachindividual patent, publication, or application was specifically andindividually incorporated herein by reference.

The foregoing description is illustrative of particular embodiments ofthe invention, but is not meant to be a limitation upon the practicethereof.

The foregoing discussion should be understood as illustrative and shouldnot be considered limiting in any sense. While the inventions have beenparticularly shown and described with references to preferredembodiments thereof, it will be understood by those skilled in the artthat various changes in form and details may be made therein withoutdeparting from the spirit and scope of the inventions as defined by theclaims.

The corresponding structures, materials, acts and equivalents of allmeans or steps plus function elements in the claims below are intendedto include any structure, material or acts for performing the functionsin combination with other claimed elements as specifically claimed.

Finally, it will be understood that the articles, systems, and methodsdescribed hereinabove are embodiments of this disclosure—non-limitingexamples for which numerous variations and extensions are contemplatedas well. Accordingly, this disclosure includes all novel and non-obviouscombinations and sub-combinations of the articles, systems, and methodsdisclosed herein, as well as any and all equivalents thereof.

1. A method to synthesize lithium iron phosphate, comprising: forming amixture by mixing spheniscidite, a lithium source, a dopant, a carbonsource, and a solvent to form a slurry, wherein the spheniscidite isderived from an iron source, an ammonium source, and an oxidant; millingthe mixture; drying the milled mixture; and firing the dried mixture toobtain lithium iron phosphate.
 2. The method of claim 1, wherein thefiring the mixture includes firing the mixture in an inert atmosphere.3. The method of claim 1, wherein the spheniscidite is plate-shaped. 4.The method of claim 1, wherein the solvent is an alcohol or water. 5.The method of claim 1, wherein the lithium source is one or more ofLi₂CO₃, Li₂O, LiOH, LiF, and Lil.
 6. The method of claim 1, wherein thedopant is one or more of V, Nb, Ti, Al, Mn, Co, Ni, Mg, and Zr.
 7. Themethod of claim 1, wherein the dopant comprises up to 10 molar % thelithium iron phosphate.
 8. The method of claim 1, further comprisingformulating the obtained lithium iron phosphate into an electrode usingconductive additive and a polymeric binder.
 9. A method to synthesize acathode active material, comprising: synthesizing spheniscidite from anammonium source, iron source, and an oxidant; forming a mixture bymixing synthesized spheniscidite, a lithium source, a dopant, a carbonsource, and a solvent to form a slurry, wherein the synthesizedspheniscidite is plate-shaped; milling the mixture; drying the milledmixture; and chemically reducing the dried mixture via a temperatureprogrammed reaction under nitrogen to obtain the cathode activematerial.
 10. The method of claim 9, wherein the carbon source is one ormore of PVB, citric acid, sugar, PVA, or glycerol.
 11. The method ofclaim 9, wherein the obtained cathode active material is LiFePO₄. 12.The method of claim 9, wherein the obtained cathode active material hasa spherical secondary particle shape when the solvent is water.
 13. Themethod of claim 9, wherein the obtained cathode active material has aprimary particle size between 20 nm and 80 nm when the solvent is one ofwater or alcohol.
 14. The method of claim 9, wherein the obtainedcathode active material includes less than 5 weight percent of a phasethat does not store ions.
 15. A method to synthesize a material for anelectrode material, comprising: selecting a solvent from one of water oralcohol; forming a mixture by mixing spheniscidite, a lithium source,and the selected solvent to form a slurry; milling the mixture; dryingthe milled mixture; and firing the dried mixture to obtain the electrodematerial composed of primary and secondary particles, wherein a shape ofthe secondary particles is based the selection of solvent.
 16. Themethod of claim 15, wherein the shape of the secondary particles isspherical when water is selected.
 17. The method of claim 16, whereinthe secondary particles have a d50 particle size in a range of 5 micronsto 13 microns.
 18. The method of claim 16, wherein the secondaryparticles have tap density in a range of 0.8 g/mL to 1.4 g/mL.
 19. Themethod of claim 15, wherein forming the mixture further includes mixinga dopant and a carbon source with the spheniscidite, the lithium source,and the solvent.
 20. The method of claim 15, wherein the sphenisciditecomprises from about 25 wt. % to about 30 wt. % iron, 15 wt. % to about20 wt. % phosphorous, from about 4.6 wt. % to about 5.0 wt. % ammonium,and wherein a molar ratio of phosphorous to iron is from about 1 toabout 1.25.